Velocity-meter.



No. 744,909. PATENTED NOV. 24, 1903. G. DETTMAR.

VELOCITY METER.

APPLICATION FILED MAY 4, 1903.

N0 MODEL.

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UNITED STATES I atentecl llTovember 24, 1903.

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GEORG DETTMAR, OF FRANKFORT-ON-THE-MAIN, GERMANY, 'ASSIGNOR TOELECTRIOITATS AOTIEN GESELLSOHAFT, VORM. W. LAHMEYER & CO., OFFRANKFORTON-THE-MAIN, GERMANY.

VELOCITY-METER.

SPECIFICATION forming part of Letters latent No. 744,909, dated November24, 1903.

Application filed May 4. 1903. Serial No. 155,665. (No model.)

To aZZ whom/it may concern.-

Be it known that I, GEORG DETTMAR, a sub ject of the German Emperor,residing and having my postoflice address at 45 Hoechsterstrasse,Frankfort on the Main, Germany, have invented certain new and usefulImprovements in Velocity-Meters, of which the following is aspecification.

This invention relates to means for applying the variation of theinduction of induction-coils which inclose a magnetic circuitforexample, choking-coils-to the measurement of the velocity of bodies. Itis already known that the variation of the induction of such coils canbe effected by providing them with a second winding, which is traversedby a direct current of electricity, so that by varying the excitation itis possible to vary the field strength, and consequently the induction,of the coil. If, for instance, the magnetic field be completelysaturated by the directcurrent winding, the induction is almost ml; butif the direct-current circuit be entirely switched out the inductionattains its maximum value. It is then possible to adjust the apparatusfor any required value of induction. The said variation can be carriedout in practice in various ways and is especially valuable where aninductioncoil having a variable induction has to be used.

The foregoing can be applied with great advantage to the tachymeterswhose constru 0- tion is based on electrical principles and in which thebody in motion is caused directly or indirectly to'periodically make andbreak an electric circuit having induction, the amplitude of oscillationof a measuring instrument included in this circuit giving themeasurement of the velocity of the moving body. The application of thisinvention to tachymeters of this character renders their indicationsindependent of the fluctuations of pressure whatever the origin of thesefluctuations may be.

The accompanying drawing illustrates an application in accordance withthe present invention.

The moving body whose velocity is to be measured is provided with acurrent-interrupter U, connected to the primary winding P of astandardized measuring instrument indicating the speed of thecurrent-interrupter. The primary winding P and interrupter U are inparallel with a shunt resistance N and in series with a reducingresistance V. In the same circuit as the first-named resistance V is acompensating coil Q, arranged on the transformer, which coil Q istraversed by an uninterrupted direct eurrect, the primary coil P and thesecondary coil of the measuring instrument being traversed by currentsof fluctuating intensity while the interrupterU is rotating. The workingof this arrangement as regards the primary and secondary coils and theircooperation with the current-interrupter and the result obtained by themeasuring instrument M will be easily understood from the foregoingdescription. The purpose which the reducing resistauceV and the shuntresistance W fulfil in this arrangement is to avoid the sparking causedat the interrupter by the first-named resistance, while the seeond-namedresistance increases the accuracy of the measuring instrument.

The operation of the arrangement is as follows: The voltage of thesecondary coil depends on the variation in the number of lines of forcepassing through the transformer T in a unit of time, and this variationitself depends on the number of ampere -turns in the primary coil P, thefrequency being presumed to be constant. Disregarding for the time thecompensating resistance Q and supposing that the voltage at theterminals varies between [M and M, there will be a correspondingvariation of ampere-turns in the interrupter-circuit, which variationwill be from zero to the maximum, and there will also be an induction inthe transformer which will vary between zero and a maximum value (B) ofthe induction, corresponding to a maximum value (A XV) of the number ofampereturns. If now the potential at the terminal varies, the number ofthe ampere-turns varies also in the primary, together with the induetionon the transformer T. In fact, all the elements of the circuit will varyin the same sense as the terminal voltage-that is to say, with equalnumber of revolutions or interruptions the secondary voltage-increasesand mo decreases as the terminal voltage increases and decreases, whilethe oscillation of the measuring instrument M likewise varies with theterminal voltage. If now the aforesaid compensating coil Q be placed inthe transformer T, as shown on the accompanying diagram, the number ofampere-turns of the compensating coil acts additively with the variablenumber of ampere-turns of the primary P of the transformer. Theinduction of the transformer then does not fluctuate between zero andthe maximum value, but varies between a minimum and a maximum value,which I will call B minimum and B maximum, respectively. The higher thedegree of saturation arising from the compensating coil Q the lesser thedifference between B minimum and B maximum for various points of themagnetizing curve obtained for various terminal voltages. Thisdifference becomes smaller as the magnetizing which takes placecorresponds to the straight portion of the magnetizing curve. It istherefore possible to so arrange the apparatus that a variation ofvoltage taking place within extended limits remains without influence,as it is possible, owing to the shape of the magnetizing curve, tomaintain constant the difference between 13 maximum and B minimum forterminal voltages varying between wide limits. The secondary voltage,which for equal number of revolutions of the interrupter depends solelyupon the aforesaid difference, will therefore remain constant.

The measuring instrument M is indicated diagrammatically and may be ofany of the well known types-as, for instance, one known as theheating-wire instrument or electromagnetic instrument or any otherequiva lent and well-known instrument.

Having now particularly described and ascertained the nature of the saidinvention and in what manner the same is to be performed,

.circuit, and a measuring instrument connected with the secondarywinding of the transformer, substantially as described.

2. A velocity-meter comprising a transformer, an induction-circuitincluding the primary winding and a, compensating winding of thetransformer, means for making and breaking said circuit, a shuntresistance in parallel with said means, and a measuring instrumentconnected to the secondary winding of the transformer,substantially asdescribed.

A velocity-meter comprising a transformer, an induction-circuitincluding the primary winding and a compensating winding of thetransformer, and means for making and breaking said circuit, aresistance in shunt to said means, a reducing resistance in series withsaid means, and a measuring instrument connected to be operated by thetransformer, substantially as described.

In testimony whereof I have signed my name to this specification in thepresence of two subscribing witnesses.

GEORG DETTMAR.

Witnesses:

MICHAEL VoLK, JEAN GRUND.

